Findings from a study, which appear in the Annals of the Rheumatic Diseases, suggest that smoking accounts for more than a third of cases of the most common form of RA and for more than 50% of RA diagnoses among people who are genetically susceptible to the development of this disease.

RA is an autoimmune disease that occurs when the body’s immune system engages in friendly fire against the joints and bones, resulting in inflammation, pain, and mobility problems as the disease progresses.

The effects of smoking are not as pronounced on RA risk as they are on lung cancer risk. Studies show that smoking is responsible for about 90% of lung cancer cases, but smoking’s effect on RA is similar to its effect on heart disease risk.

According to the new study, RA risk is related to how much a person smokes, how long a person smokes, and the presence of certain antibodies in the blood that are associated with RA, namely ACPA antibodies.

“The study adds an estimate on how important smoking is in the occurrence of RA,” says study author Henrik Källberg of the Institute of Environmental Medicine at Karolinska Institute in Stockholm, Sweden, in an email. “We believe that smoking is a causative risk factor which probably works as a spark that starts the autoimmunity fire."

“Smoking changes proteins which start the immune system’s reaction against the own body [and] this reaction starts much easier when a certain genetic factor is present.”

Quit Smoking Now

Swedish researchers analyzed data from the Swedish Epidemiological Investigation of Rheumatoid Arthritis (EIRA) on 1,204 people with RA and 871 people without RA who were aged 18 to 70 from 19 clinics throughout Sweden. Participants were asked questions regarding the present and previous smoking history and how many cigarettes they smoked per day. Study participants also underwent blood tests to determine their genetic risks for developing RA.

Smoking plays a role in about 33% of cases of RA among people with detectable levels of ACPA in their blood, and one in five cases of RA in general. Specifically, people with RA who smoked a pack a day for more than 20 years were more than 2.5 times as likely to be antibody positive.

The increased RA risk conferred by smoking was more pronounced among men than women, the study showed.

Quitting smoking did have some effect on reducing RA risk, the study showed.

Among the heaviest smokers, however, the risk of RA remained high even 20 years after they quit smoking.

The new findings “may provide a rationale for specific counseling against smoking for individuals with a family history of RA,” Källberg and colleagues conclude. “There are many reasons for the medical community to communicate the known facts on smoking and RA with the aim of reducing the incidence of smoking and preventing.”

More Research Needed on Smoking and RA

Ted R. Mikuls, MD, a rheumatologist at the University of Nebraska Medical Center in Omaha, says the new study validates earlier research on how smoking affects RA risk including a study from his own group that showed cigarette smoking increases the risk of RA among African-Americans.

“Smoking is the environmental risk factor that has most consistently been linked to RA,” he says. “For now, it is the only modifiable risk factor that has been consistently linked to this condition, adding weight to public health measures aimed at reducing smoking prevalence.”

Precisely how smoking affects RA risk is not well understood, he tells WebMD in an email. “The short answer is that we’re not sure exactly what the mechanisms are that link cigarette smoking to an increased RA risk,” Mikuls says.

“Understanding this link better may provide us with much needed insight into how RA starts and may provide us avenues for treatment or even means of prevention,” he says. “Patients know that smoking contributes to other health risks, but often discussing the link with their arthritis provides added incentives to quit.”